The middle boards in a panel always see higher temperatures than the boards along the outside edges, especially if they are on the sides and in contact with the conveyor. Fixtures that have "finger" contact only suspend the board, and then the only heatsinking occurs right around the finger itself.
My experience with these type of caps is that they also have a 2% silver content in the terminations as supplied by the vendor. So between the higher heat seen near the center of the panel, and the 2% silver discoloration, their appearance will be different from those on the outer CCAs in the panel.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jim West
Sent: Tuesday, March 06, 2012 12:03 PM
To: [log in to unmask]
Subject: [TN] Capacitors end termination discolored.

Hi all,

Take a look at the photo's at the below links (one shows picture of a new cap).  I'm trying to figure out why the end terminations of a tantalum capacitor (C37 and C38) are coming out of the reflow discolored.  In our process, the middle boards of our panel have the discolored terminations.  The boards on the outside of the panel are all fine.  I think it's a heat related issue, but I don't know why only the middle boards are affected.  All the solder joints are looking fine as well (even on the discolored terminations).

Any thoughts as to what might be happening?  In your opinion, would your reject these?

http://stevezeva.homestead.com/Discolored_Tant.jpg

http://stevezeva.homestead.com/New_Tant.jpg

Jim West







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